Field of the Invention
The present invention relates to an image pickup apparatus including a plurality of imaging units and a control method for the same.
Description of the Related Art
In recent years, research has been done on image pickup apparatuses utilizing a technology called Computational Photography. With this technology, in addition to simple data such as the brightness and color of an image, information such as an angle of incidence, a depth, and the like of light from an object, which have not been recorded in the conventional image pickup apparatuses, are captured in an imaging element and are stored with image data, so that various types of processes are performed by an image processing LSI. With the use of these pieces of information, a focus, a depth of field controlled by the iris, a focused position, and the like, which have been uniquely determined upon completion of imaging, can be correctly reproduced by image processing after photography. There has been proposed an image pickup apparatus that has a function capable of changing a focal position by post-processing of data of a captured image by recording light beam information called as light field (hereinafter abbreviated as “LF”).
As a representative example of obtaining LF data, there is a method for obtaining an image from multiple viewpoints. For example, one image pickup apparatus obtains a plurality of images by varying the focal position and records data as a single image, so that the focused position of the image can be freely changed by image processing at a later time. Data of a plurality of images is obtained by moving the camera in the horizontal direction or the vertical direction, so that distance information (depth) about an object can be obtained from the parallax in images. In this case, there is a disadvantage in that LF data cannot be effectively obtained for a dynamic object because of use of a single image pickup apparatus (imaging element). Thus, there has been proposed a method of using a plurality of imaging elements or image pickup apparatuses in order to obtain an image from multiple viewpoints (Japanese Patent Laid-Open No. 2008-257686). The plurality of imaging elements or image pickup apparatuses are arranged in the form of an array, so that simultaneity can be provided for the obtained images and the amount of information about LF data can be increased by obtaining data of a plurality of images.
If all the imaging systems include a zoom lens in the system including a plurality of imaging elements or image pickup apparatuses, this results in an increase in size of a barrel unit, an increase in power consumption, the complexity of lens control, and the like. As a solution, in the system shown in FIG. 1, imaging units each of which is a combination of each of a plurality of lenses A to D with different focal length and an imaging element corresponding thereto are arranged in the form of a matrix. Optical zoom by the switch control of the lenses is used in combination with electronic zoom by image processing, resulting in a reduction in size, low power consumption, and the simplicity of lens control. However, in order to keep the dimension of an object image constant upon switching a lens with different focal length, the magnification ratio of electronic zoom must be changed abruptly in synchrony with the switching of a lens. Thus, an abrupt change in resolution remains as an undesirable event. As a technology for suppressing an abrupt change in resolution, Japanese Patent Laid-Open No. 2007-329685 discloses a technology that temporarily shifts the control position of the focusing lens by changing an edge enhancement filter coefficient when the number of read lines of the imaging element varies with drive switching of the imaging element.
In the technology disclosed in Japanese Patent Laid-Open No. 2007-329685, an edge enhancement filter coefficient increases when the magnification ratio of electronic zoom is high, resulting in a reduction in the S/N (signal to noise) ratio of an image. When an edge enhancement filter coefficient changes abruptly, an abrupt change in image quality cannot be suppressed due to an abrupt change in the S/N ratio of an image. In addition, the position of the focusing lens must be changed by driving the mechanism. Thus, a long time may be taken from the start of controlling the position of the lens to the completion of actual movement of the lens to a desired position. Therefore, it is difficult to realize a resolution equivalent to the resolution prior to change immediately after the driving of the imaging sensor is switched.